KABUL, April 9 (Reuters) - A frontrunner to succeed Hamid Karzai as Afghanistan's president voiced the possibility of teaming up with a rival on Wednesday but ruled out forming a coalition government in order to avoid a second-round runoff.

Afghanistan voted in a landmark presidential election last weekend which, if successful, will usher in the first democratic handover of power in the country's history as Karzai prepares to step down after more than 12 years in office.

Preliminary tallies put former foreign minister Abdullah Abdullah in the lead in parts of the capital Kabul. But it could be weeks before a countrywide winner emerges from the field of eight candidates because Afghanistan's rugged terrain and weak infrastructure make tallying all the ballots so difficult.

Speaking to Reuters at his home on Wednesday, Abdullah said he met his rival, another ex-foreign minister Zalmai Rassoul, shortly after the April 5 election to discuss possibilities.

"I had asked for that meeting. We had a good discussion. I will not go into the details of it but you can imagine that at this stage we are not talking about the weather or leisure," he said.

"We have been in the same government in the old days, we have been friends for many years. So that is the personal part of it. The rest of it depends on the common understanding of certain subjects and certain policies."

Abdullah has been noticeably more critical of the other frontrunner, ex-finance minister Ashraf Ghani. Asked if he could work with Ghani, he said with a tinge of sarcasm: "Mr Ghani has declared himself the winner. So let him absorb the victory."

If none of the candidates gets more than 50 percent, a runoff will have to be held, at the earliest in late May, considerably prolonging the wait for a winner to be declared.

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Western powers, who are withdrawing most of their forces from Afghanistan this year, are watching the process intently after a messy presidential election in 2009 resulted in allegations of mass fraud and ballot stuffing.

Foreign donors, who are hesitant about bankrolling the Afghan government after the bulk of NATO troops leaves, will also closely scrutinise the composition of the country's future government to decide if they can work with the new team.

The protracted nature of the vote-counting process, which requires ferrying ballot boxes from remote parts of Afghanistan by donkey or mule, has sparked speculation that some of the candidates might opt for a closed-door deal to avoid a runoff.

It was not clear what any such deal would entail.

Abdullah, a trained ophthalmologist turned anti-Soviet resistance fighter, ruled out the possibility of a coalition government.

"The team which will govern Afghanistan will not be an exclusive team. The inclusiveness is part of our strategy," he said. "But that does not suggest that we are making a coalition government in order to avoid a runoff or anything like it."

Abdullah, who failed in his presidential bid in 2009 and complained the poll was marred by massive ballot box stuffing, deployed thousands of observers across Afghanistan to monitor the election this time around.

But he declined to say if he had scored above 50 percent based on their observations.

"From their observations on the ground and also from the tallying that we have been doing on the basis of the results sheets that we have received through our observers and monitors from all around the country, it sounds good for us," he said.

Asked if he believed the election would be decided in one round, he said: "Hopefully. Most probably." (Editing by Tom Heneghan)